Cancer is one of the most deadly diseases in the present world. Facing cancer, most people believe surgery, chemotherapy or radiation therapy is the only possible solution. However, not all cancer patients are suitable for surgery, and cancer metastasis may cause the failure of surgery treatment. The chemotherapy or radiation therapy may lead to large damage of normal organs and less effect on cancer niche. Furthermore, hypoxic tumor cells may demonstrate an inhibition of cell cycle progression and proliferation, and hence may be relatively resistant to many anticancer drugs that target rapidly dividing cells. Thus, in solid tumors, hypoxic regions create a further problem as they are resistant to many treatments [1] and are linked to more malignant phenotypes [2].
Intentional use of bacteria in cancer treatment can be dated to the late 19th century with even earlier anecdotal reports of bacterial efficacy in treating cancer [3, 10, 11]. The first reported deliberate attempt at using bacteria (Streptococcus pyrogenes) to treat an inoperable sarcoma also demonstrated the inherent danger of the technique. Whilst the tumor and lymph nodes reduced appreciably, the patient died of infection within 9 days of treatment [3, 10, 11]. On the other hand, targeted cancer therapy, gene therapy and cancer vaccine are all based on the transfection technique. The most critical issues associated with these therapeutic strategies are the safety of vectors. Viral vectors are most widely used delivery vectors, however, they are not easy to be eliminated, potentially tumorigenic with limited capacity. Accordingly, non-viral vectors with larger capacity and safe manipulation, such as bacterial vectors, are a promising approach to develop new delivery systems.
Consequently, much recent work on bacterial therapies for cancer has focused on non-pathogenic strains or the need to attenuate bacteria for use in model systems and humans. Bifidobacteria are non-pathogenic obligate anaerobes and have been successfully used to target tumors and as a therapeutic vectors but do not appear to have an oncolytic effect [8, 12-14].